SAP SE11

It opens the ABAP Dictionary to view/maintain database tables, data elements, domains, views and other dictionary objects, the reference for SAP’s data structures.

• Object type (table, data element, domain, view).
• Table fields, data types, keys and indexes.
• Technical settings (buffering, size category).
• Where-used and documentation.

• Use SE11 to understand a table’s structure before querying it.
• Follow a field to its data element and domain.
• Check indexes when troubleshooting query performance.

• Editing dictionary objects without proper change management.
• Confusing transparent tables with pooled/cluster tables.
• Missing authorization to change dictionary objects.

• Writing a SELECT after reading the field list but not the key. Access outside the key on a large table is a full scan, and the code passes review because it looks correct.
• Missing that a field's meaning lives in its domain. The fixed values behind a status field are where the codes are defined, not on the table itself.
• Ignoring the append structure. Customer fields added to a standard table live there, so a definition that looks standard may not be what your system holds.
• Assuming a view holds data. A database view reads its underlying tables at runtime, so its performance is theirs.
• Adding an index to fix a slow query. Every index costs on write, and the cause is more often a predicate that cannot use the key you already have.